An electromechanical power transfer system of the hybrid type, wherein a prime mover such as a gas turbine engine simultaneously generates AC and DC type electrical power, is particularly useful for aeronautical applications. Such applications generally require 230 V 400 Hz three phase AC as well as positive and negative 270 V DC.
In aeronautical applications, electromechanical power transfer systems convert power from variable speed prime movers, generally of the gas turbine type, to electrical power for electrical that require a high degree of regulation. Such power transfer systems usually convert mechanical power from the prime mover to electrical power by way of a brushless dynamoelectric machine, such as a wound field synchronous machine (WFSM) that has the ability to regulate its electrical output when integrated with a suitable system controller. Alternatively, regulated permanent magnet machines that are also capable of developing a highly regulated power output are becoming available for this purpose. Such dynamoelectric machines inherently generate multiphase AC power, generally of the three-phase type.
Hybrid electromechanical power transfer systems according to the prior art generally employ a three-phase rectifier that converts AC generated by the dynamoelectric machine to DC that it couples to a DC bus and a three-phase pulse width modulated (PWM) inverter. These systems require a large size DC link capacitor to decouple generator variable frequency AC power and constant frequency inverter output AC power. It is possible to generate variable frequency AC power with two back-to-back converters to eliminate a bulky DC link capacitor.
Using a high-speed brushless dynamoelectric machine for electrical power generation results in reduced size and weight of the dynamoelectric machine. In some cases, high-speed dynamoelectric machines may directly couple to a prime mover, such as a gas turbine engine, thereby eliminating a reduction gearbox that results in further reduction of size, cost and weight of total electromechanical power transfer system. Using a generator with a high number of poles and increased operating speed enables generation of a high frequency output of 4,000 Hz or more. An AC bus for such high frequency AC power is not suitable for power distribution in an aircraft due to EMI constraints and requirements. However, it may be attractive in a combination with matrix converter topologies that eliminate bulky DC bus capacitors resulting in reduction of size and cost for power electronics.